Advanced Semiconductor Technologies

Advanced Semiconductor Technology

As a chip independent supplier of power modules, Vincotech is able to offer power module solutions with the best combination of semiconductors available on the market.For example are the new silicon carbide (SiC) MOSFET technologies available from 5 different sources. But Vincotech is not only able to provide the optimal semiconductor combination but also to provide and benchmark advanced technologies as SiC with best in class Si solutions.

SiC status

Two factors are shaping the development of advanced power conversion systems - increasingly stringent standards for energy efficiency, especially in solar and UPS applications, and the need to decrease the overall system's costs for the customer. These two goals are rather ambitious, at least for power semiconductors based on conventional silicon technology and with limited switching capabilities. The solution is the use of wide band power semiconductors as SiC (silicon carbide).

It offers:

High breakdown field strength (tenfold that of Si)

A wide bandgap (threefold that of Si)

High thermal conductivity (threefold that of Si)

These properties are conducive to applications that demand greater efficiency in a smaller footprint and operate at higher frequencies and temperature.

Vincotech successfully rolled out the first standard power modules with SiC Schottky diodes ten years ago. SiC Schottky diodes have practically no reverse recovery charge, which reduces switching losses in the diode itself and even in IGBTs when these transistors are used as commutation partners. SiC Schottky diodes are the solution of choice for many of today's applications.

A comparison of Si and SiC components

This assessment is based on a booster topology. One possible point of application is on the DC input side of inverters in photovoltaic systems.

The first step to improve efficiency is to replace the Si diode with a SiC diode. Figure shows the efficiency curve as a function of the input current (power) in a comparison of modules with IGBT switches and Si or SiC diodes. Efficiency/losses increase/decrease respectively with the SiC diode even at switching frequencies > 4 kHz. Losses can be reduced to 50 % from 1.6 % to 0.8 % at 16 kHz and 5A input current. Further reduce of the losses by 37 % to 0.5 % can be achieved at the same input power and same switching frequency by using a SiC MOSFET in place of an IGBT. This is the second step to increase efficiency.

The benefits of the SiC MOSFET are even more striking at switching frequencies > 32 kHz. Given the same input current and a switching frequency of 64 kHz, efficiency increases and losses are reduced by just under 35 %. The effect is even more pronounced at higher input currents, but measures must be taken to ensure good cooling. These simulations were carried out with a constant heat-sink temperature of 80 °C. The physical limitations of Si technology are soon evident in applications demanding great efficiency and high switching frequencies. It is equally evident that SiC components will drive this market.

The following figures also show the benefits of using SiC components rather than Si components in performance-driven applications. Given the same losses – for example, 50W of total dynamic and static losses – and a switching frequency of 16 kHz, output power can be increased by up to 85 % when using SiC diodes instead of Si diodes. In this case, output power is commensurate with input current. Given the same switching frequency, output power can be increased up to 50 % by using a SiC MOSFET in place of an Si IGBT. In this case, the combination of IGBT switch and SiC diode outperform the SiC MOSFET and SiC diode pairing because the IGBT's conduction losses are lower than those of the SiC MOSFET.

Another interesting comparison looks at how total losses relate to switching frequencies. Compared to the Si diode with IGBT switch, the SiC-diode-with-IGBT combination's switching frequency can be increased from 16 kHz to > 48 kHz with switching losses remaining the same (at input current 5 A). The SiC diode/ SiC MOSFET twosome's switching frequency may even be increased to over 100 kHz. And as the switching frequency rises, the size and cost of the inductance for the overall system can come down. In the final reckoning, losses can be decreased by more than 80 % with SiC components rather than Si components. This, in turn, reduces the effort and cost of cooling. The benefits shown here also go a long way in helping engineers miniaturize end products and therefore cut costs. However, a quantitative assessment of the cost reduction also has to consider other factors and the challenges inherent in using SiC technology.